Method of encapsulating coils



July 24, 1962 E. H. ANDERSON ETAL METHOD OF ENCAPSULATING COILS Original Filed Oct. 11, 1957 ATT'YS 4- Claims. (CI. 18-69) This invention relates to electric coils, and more particularly to an encapsulated coil and method of making the same.

This application is a division of Anderson and I-Ieidorn application, Serial No. 689,651, filed October 11, 1957, for Encapsulated Coil and Method of Making Same.

The technique heretofore employed in the manufacture of encapsulated electric coils has been to wind a coil of wire onto a spool or bobbin comprising a center hollow core equipped at its ends with laterally extending flanges. After the coil has been wound between the flanges, terminals mounted upon one or both of the flanges, and the ends of the coil connected to the respective terminals, the product is then dipped into a dielectric maintained in liquid form completely to coat the exposed surfaces of the spool and wire and a portion of the terminals. After such bodily dipping of the coils into the dielectric, which may be carried out by first positioning the coils on vertical shafts provided by a movable carrier, the spools and carrier are withdrawn from the dielectric, and the coating is subjected to heat or is otherwise cured to harden the same.

This technique has been followed in commercial practice irrespective of whether the bobbin or coil form is made of paper, plastic or other material, and regardless of the configuration of the coil form, i.e., tubular polygonal, or other. It will be apparent that mounting the coil upon vertical shafts provided by the carriers has been advantageous, for such shafts substantially fill the respective openings through the center cores and thereby prevent to a large extent the entrance of the liquid dielectric thereinto, for such openings must be unobstructed to receive iron cores.

Even though this practice has been followed exclusively, it has a number of serious disadvantages, among which is the relatively long time cycle required to mount the coils in the carriers, dip the same into the liquid dielectric, thereafter cure the dielectric and remove the coils from the carriers. Another disadvantage results from the wastage of dielectric material that necessarily attaches to dipping or submerging operations. Furthermore, the end product is crude in appearance, but more important, has a dielectric coating of uneven thickness with voids throughout and with only the most tenuous bond with the coil form. Such disadvantages, it will be appreciated, adversely influence the electric characteristics of the completed coil.

The invention herein contemplates the encapsulating of a coil form therefor with a resinous insulating material which is compatible with the insulation covering the coil turns, and introducing the encapsulating material into a mold cavity where the coil and form are positioned. The encapsulating material is introduced to the cavity as a liquid at an elevated temperature of a value sufficient to cause the insulation of the coil turns and the coil form to merge with the encapsulating material, and substantially obliterate any distinction between the two materials. A feature of the invention resides in nicely controlling the duration of the elevated temperature of the encapsulating material for a time suflicient to provide merging of the two materials, but not sufiicient to injure the insulation material of the coil turns and the coil form.

well known in the art.

Accordingly, the object of this invention is to provide an encapsulated electric coil of improved character, that overcomes the disadvantages inherent in the prior art structures. Another object of the invention is in the provision of an encapsulated coil form andmethod of making the same, having a dielectric coating of predetermined and uniform thickness, and which has a neat, finished appearance. Still another object is in the provision of an electric coil and method of making the same, wherein a bobbin having a coil bf wire wound thereon is encapsulated with a dielectric material so intimately bonded to the bobbin that substantially no distinction exists therebetween, whereby an integrated encapsulation of the entire wire coil is afforded- Still a further object of the invention is to provide an encapsulated coil and method of making the same, where in a coil of wire is wound upon a thermoplastic coil form or bobbin, and in which a thermoplastic dielectric is molded thereabout at a temperature sufficient to soften the coil form, the coil form and encapsulating dielectric being of the same or other suitable compatible material whereupon the encapsulating dielectric and coil form unite, with the result that a unitary or integral encapsulation of the electric coil is provided. Additional objects and advantages of the invention will become apparent as the specification develops.

An embodiment of the invention is illustrated in the accompanying drawing, in which- FIGURE 1 is a perspective view of an encapsulated electric coil embodying the invention; FIGURE 2 is a longitudinal sectional view taken along the line 22 of FIGURE 1; FIGURE 3 is a longitudinal sectional view of the cavity portions of an injection mold, and illustrates one step in the method of making the encapsulated coil; FIGURE 4 is a longitudinal sectional view similar to that of FIGURE 3, but showing the mold sections in closed position and with the dielectric material being inserted into the cavities thereof.

The electric coil illustrated in FIGURES 1 and 2 embodies the invention, and is denoted in its entirety by the numeral 10. This specific coil, which is exemplary only, comprises a Wire coil 11 defined by winding an electric wire conductor upon a mandrel thereafter removable therefrom, or upon a coil form or bobbin in a manner Surrounding the coil 11 is an encapsulating body 12 of dielectric material. The encapsulating body of the structure shown in FIGURE 2 has a central opening or passage 13 extending therethrough, which is adapted to receive a magnetic core where such is necessary.

Extending outwardly from the encapsulating body 12 are a pair of terminals 14 and 15 which are electrically connected to the ends of the coil 11, and are partially covered by the encapsulating material as shown at 16 and 17. It will be understood that the terminals 14 and 115, as separate structural components, could be and often are omitted and leads (such as the ends of the wire coil) used instead.

It will be apparent that the electric coil 10 in the form shown in FIGURES 1 and 2, is a simple inductance whereby the terminals or leads l4 and 15 are the only electrical connections that need be made thereto. In the event, however, that the component is a transformer rather than an inductance, either an auto winding or a plurality of wire coils defining conventional primary and secondary windings will be provided. In either case additional leads or terminals will be necessary and these will be connected to the various wire coils.

It will be noted in the specific structure shown that a substantially integral encapsulating body 12 surrounds the wire coil 11, thereby completely enclosing the same. Not only is there no discontinuity throughout the encapsulating body, but it has uniform thickness. That is to say, in any selected area of the coil where it is desired to have the same amount of thickness of coating over the entire extent thereof, such thickness can be and is provided. In many instances, it may be advantageous to vary the coating thickness fromlocation to location on the electrical component or to have certain parts uncoated (the terminals 14 and 15, for example), and such arrangements are readily and accurately afforded. The point of importance is that the encapsulation can be controlled precisely both as to thickness and location, in contrast to the non-uniformity inherent in the prior art structures. Further, it is also an attractive product, as is made apparent by the FIGURE 1 illustration. Moreover, since there are no voids throughout the encapsulating body, and because it has a uniform thickness, the electrical performance of the coil is much superior to those which have such shortcomings.

The method for encapsulating the Wire coil 11 is shown in FIGURES 3 and 4, and the starting product comprises the wire coil 11 which may be wound upon a spool or bobbin 18 defining a coil form having a central hollow core 19. Quite commonly, as is illustrated, the bobbin may have end flanges 2t) and 21 formed integrally therewith or separately secured thereto. The wire coil 11 is Wrapped about the center core 19 between the end flanges in a conventional winding operation, and the terminals 14 and are riveted or otherwise rigidly secured to the flange 21 with the respective ends of the wire coil connected thereto. The method is applicable in connection with bobbins that do not employ end flanges, and also with self-sustaining wire coils.

The bobbin 18 is formed preferably of a material that will soften and commence to melt at ordinary injection molding temperature (which may vary through a range of about 300 to 800 R), such as the thermoplastic which has good dielectric properties. Examples of these are nylon, Cycolac, cellulose acetate, etc.

The partially completely coil, as shown in FIGURE 3, is placed within an injection mold that comprises separable mold sections 22 and 23. These mold sections provide, respectively, cavity sections 24 and 25; the first of which is cylindrical in the specific illustration and has an opening of lesser diameter communication therewith that slidably receives a holder 26, comprising a piston or rod 27 having a centering pin 28 of reduced diameter extending outwardly therefrom through the center of the cavity section 24. The piston at the opposite end thereof, not shown, is arranged with some suitable means of applying force thereto for urging the same toward the right (as viewed in FIGURE 3) properly to position the coil within the cavity and thereafter maintain it in such position against the pressure exerted by the fluid encapsulating material. Affixed to the mold section 22 is a backing plate 30 that has a central opening therethrough which also slidably receives the piston 27.

The cavity 25 in the mold exemplification shown, has the same diameter as that of the cavity 24 but is relatively shallow with respect thereto. Communicating with the cavity 25 is a pair of stepped passages or recesses 31 and 32 adapted to receive the terminals 14 and 15 therein. The portions of the passages that are adjacent the cavity section 25 are relatively wide with respect to the terminals, but the stepped end portions 33 and 34 thereof are dimensioned so as to snugly receive the terminals therein. A backing plate 35 is atfixed to the mold section 23.

The injection mold thus defined in terms of the components thereof pertinent to the instant invention, may otherwise be conventional and functions to receivethe fluid encapsulating material in the cavity thereof to mold the material into a predetermined configuration. The material may be inserted into the mold through a gate 33 defined by passage segments 36 and 37 provided respectively in the mold sections 22 and 23. Ordinarily,

the mold will be chilled as by means of liquid circulation through coolant passages 29. The mold sections are adapted to be brought together as shown in FIGURE 4, to define a unitary molding cavity, and such operation with respect to the coil will now be described.

First, the bobbin 18 with the wire coil 11 wound thereon, and with the terminals 14 and 15 suitably mounted on the flange 21 in the electrical connection with the ends of the coil, is positioned with the passage 13 therethrough aligned with the centering pin 28 and with the terminals 14 and 15 aligned with the respective passages 31 and 32. The mold sections 22 and 23 are then moved into closing relation as shown in FIGURE 4, and the centering pin 28 is caused to move into passage 13 to hold the coil and insert the terminals 14 and 15 thereon into the passages therefor in the mold sections 23. After the mold sections are closed, the fluid encapsulating material enters the mold cavity by means of a gate 38, which is defined by the sections 36 and 37. The mold is maintained in closed condition until the fluid material cures, and suflicient force is applied to the holder 26 to assure s .rinkage of the fluid in the right direction. Thereafter, the mold is opened to permit removal of the finished coil product.

The curing time within the mold (which is of relatively short duration) depends upon the specific materials employed, the temperature of the incoming encapsulating fluid and the temperature at which the mold is maintained. In the case of using nylon as the fluid, it is injected into the mold at a temperature of between 525 to 625 F. and the mold is held closed for a time period of 3 to 25 seconds. It will be understood that the mold itself is always cooled, by the flow of coolant or Water through the passages 29 thereof to maintain the temperature relatively constant at between 70 to F. as in the case of a nylon plastic. I

Since the temperature of the entrant material normally averages about 6 times higher than the temperature maintained in the mold it can be likened to chilling the entrant material within seconds after the material is injected in the mold.

However, the introduction of the encapsulating material to the mold must be done at a controlled temperature, one which will provide sufficient fluidity to the encapsulating material and at the same time provide requisite softening of the coil form for the bonding of the encapsulating material thereto. Moreover, the temperature of the entrant encapsulating material must be sufliciently high to provide good coalescing with the insulation of the coil forms, yet not high enough to cause injury to the coil by reason of destroying the insulation on the wire. Also, the encapsulating material must quickly merge or coalesce with the coil and its form without altering any dimension of the coil and form, and without destroying all the identity of the insulating material of the coil forms, and the encapsulating material must be capable of resuming a structural solid state readily upon chilling of the mold. All this must be accomplished, however, in the matter of seconds.

The entrant material is required to be introduced to the cavity at a temperature which is high enough to provide the aforesaid coalescing or merging with the insulation of the coil and also its form, but not at so high a value that the identity of the coil insulation and the form is lost.

The encapsulating material welds itself to the coil form to provide a unitary encapsulation of the wire coil and where the bobbin and encapsulating material are plastics of the same general characteristics, there is a coalescence or merging of the bobbin and dielectric so that when the curing time has elapsed, the bobbin and encapsulating material are integral as shown in FIGURE 2, whereby one is substantially indistinguishable from the other.

It will be appreciated that the mold cavity may have various configurations depending upon the shape and size of the end product to be formed therein, and the shape of the cavity may be altered wherever it is desired'to have an encapsulating coating of greater thickness at one point along the coil and another point or points therealong. As stated hereinbefore, the coil may be cylindrical, as in the form shown, or it may be polygonal, and in such event, the configuration of the mold will ordinarily but not necessarily conform thereto. Furthermore, in some instances, a self-sustaining wire coil may be encapsulated by the technique disclosed that, in all events, turns out pieces quickly which are accurately and properly encapsulated and which does not result in the wastage. of encapsulating material.

It is apparent from FIGURE 4 that the fluid material fills the enlarged portions of the passages 31 and 32, and thereby encloses or encapsulates a part of each of the leads, or terminals if they are used. The centering pin 28 and piston arrangement maintain the coil in a centered relation within the mold cavity so that the fluid material can completely and uniformly surround the same, and also takes up the shrinkage thereof. As a result, the encapsulation of the wire coil has a uniform thickness throughout any selected area which lends symmetry to the electrical characteristics of the coil, resulting in improved performance thereof. Furthermore, an attractive product is formed, and the time cycle necessary to accomplish the. encapsulation is substantially reduced from that heretofore required. Moreover, the wastage of fluid dielectric is obviated.

While in the foregoing specification an embodiment of the invention as to method is described in considerable detail for purposes of making an adequate disclosure thereof, it will be apparent that numerous changes may be made in those details without departing from the spirit and principles of the invention.

What is claimed is:

1. A method of producing an encapsulated wire coil which comprises A. winding a coil of wire on a bobbin of thermoplastic material having end flanges -B. placing said bobbin in a mold cavity C. introducing thermoplastic encapsulating material of the same material of which said bobbin is made into said mold cavity, the thermoplastic encapsulating material being introduced at a temperature high enough to (1) be in a fluid state, (2) soften said flanges sufficiently to coalesce with said encapsulating material,

D. maintaining the temperature of said encapsulating material higher than the temperature required to soften the material of said bobbin for a period of time suflicient to cause coalescing of said encapsulating material with a portion of said flanges, but not long enough to destroy the identity of said bobbin, and

E. cooling said mold to a temperature lower than the solidification temperature of said thermoplastic encapsulating material.

2. A method of producing an encapsulating wire 'coil which comprises A. winding a coil of wire on a bobbin of thermoplastic material having end flanges and a hollow core,

B. placing said bobbin in a mold cavity with a centering pin in the hollow core,

C. introducing thermoplastic encapsulating material of the same material of which said bobbin is made into said mold cavity, the thermoplastic encapsulating material being introduced at a temperature high enough to (1) be ina fluidstate, (2) soften said flange sufliciently to coalesce with said encapsulating material,

D. maintaining the temperature of said encapsulating material higher than the temperature required to soften the material of said bobbin for a period of time suflicient to cause coalescing 'of said encapsulating material with a portion of said flanges, but not long enough to destroy the identity of said bobbin, and

E. cooling said mold to a temperature lower than the solidification temperature of said thermoplastic encapsulating material.

3. A method of producing an encapsulated wire coil which comprises A. winding a coil of insulated wire on a bobbin of thermoplastic material having end flanges and a hollow core,

B. placing said bobbin in a mold cavity with a mandrel in the hollow core,

C. introducing thermoplastic encapsulating material of the same material of which said bobbin is made, and which is compatible with said wire insulation, into said mold cavity, the thermoplastic encapsulating material being introduced at a temperature high enough to (1) be in a fluid state, (2) soften said flange sufliciently to coalesce with said encapsulating material,

D. maintaining the temperature of said encapsulating material higher than the temperature required to soften the material of said flanges and said insulation for a period of time suflicient to cause coalescing of said encapsulating material with a portion of said bobbin and with the insulation on the outer turns of said coil, but not long enough to destroy the identity of either said bobbin or said insulation, E. cooling said mold to a temperature lower than the solidification temperature of said thermoplastic encapsulating material.

4. The process of claim 1 further characterized in that said bobbin and said thermoplastic encapsulating material are both nylon, that said encapsulating material is injected into said cavity at a temperature of from about 525 F. to about 625 F. and that the temperature in said mold cavity is maintained between about 525 F. and about 625 F. for a period of from about three seconds to about twenty-five seconds.

References Cited in the file of this patent UNITED STATES PATENTS 2,956,312 Naimer Oct. 18, 1960 FOREIGN PATENTS 578,024 Great Britain June 12, 1946 657,821 Great Britain Sept. 26, 1951 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 4 Patent No. 3,045,290

July 24, 1962 Elr-oy H. Anderson et al.

corrected below.

Column 6, lines 7 and 33, for "flange", each occurrence, read flanges same column 6, between lines 34 and 5, insert (3) soften said in coalesce with said (SEAL) Attest:

ERNEST w. SWIDER ID L. ADD Lttesting Officer Commissioner of Patents 

